Armhole
Webster's Dictionary [1]
(1): (n.) The cavity under the shoulder; the armpit.
(2): (n.) A hole for the arm in a garment.
International Standard Bible Encyclopedia [2]
arm´hōl : The Hebrew word אצּיל , 'accı̄l , is used in Jeremiah 38:12 in the sense of armpits. When the prophet was pulled up out of the pit by ropes, the armpits were protected with rags and old garments. The meaning in Ezekiel 13:18 the King James Version (the Revised Version (British and American) "elbows," the Revised Version, margin "joints of the hands") is far from clear. The phrase is used, without doubt, of some ornament or article of dress worn by the false prophetesses and priestesses of Ashtaroth in order to allure the unwary and tempt the simple. The "pillows" were probably "amulets" supposed to have magical virtues, and worn on the arms or wrists.